Method for stabilization of manganese salts of alkylene bisdithiocarbamic acids and the products thereof



United States METHOD FOR STABILIZATION OF MANGANESE SALTS OF ALKYLENE BISDITHIOCARBAMIC ACIDS AND THE PRODUCTS THEREOF Raymond J. Sobatzki, Glenside, Pa., assignor to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Aug. 29, 1958, Ser. No. 757,939

5 Claims. (Cl. 260-429) 'ganese alkylene bisdithiocarbamate compositions which exhibit improved retention of fungicidal activity on ageing.

A further object of this invention is the preparation of manganese alkylene bisdithiocarbamate compositions which exhibit lower phytotoxicity than control samples not treated by the process of this invention. v

Another object of this invention is the preparation of manganese alkylene bisdithiocarbamates which have much less odor than control samples not treated by the process of the present invention.

A further object of this invention is the preparation of stable fungicidal compositions containing as essential active ingredient stabilized manganese ethylene bisdithiocarbamate.

While most of the metal salts of alkylene bisdithiocarbamic acid exhibit varying degrees of instability at elevated temperatures as evidenced by evolution of carbon disulfide and decreased fungicidal activity, the manganese salts appear to be even less stable than, for instance, thesodiurn or zinc salts. As an example, manganese ethylene bisdithiocarbamate has been known to undergo spontaneous combustion during manufacture and,

in isolatedcases, during storage. Although these instances of spontaneous combustion are not common, it

is known to those skilled in the art that there 'are losses of factive ingredient during storage with resultant decreased value as a fungicide. Particularly at elevated temperatures, darkening of the compound occurs and, in some cases, actual charring of the compound will be noted;

Salts of dialkyl dithiocarbamic acids also undergo de- "composition on storage which, at least on the basisof the 5 net efiects noted, appears to be the same type of reaction at fi 'fO ICC 2 to which the salts of alkylene bisdithiocarbamic acids are susceptible. In both cases, it appears to be the group N-c-s- II which is unstable as suggested by the fact that the amount of-decomposition is almost directly proportional to the amount of carbon disulfide which is evolved. Thus, a measurement of the amount of carbon disulfide evolved makes possible comparisons of the relative stabilities of various samples.

Numerous methods of improving the stabilities of metal salts of alkylene bisdithiocarbamic acids have been proposed in the prior art. Careful control of the pH of the reaction mixture throughout the reaction period is said to result in a final product with increased stability. Control of order of addition of the reactants involved is'also said to produce products with superior stability. In US. Patent 2,665,285, the use of inorganic sulfite, suchas sodium and calcium sulfites, bisulfites, or hyposulfites, is set forth as additives to increase the stability of derivatives of dithiocarbamic acids. It the suspension of the derivative of dithiocarbamic acid containing sodium hyposulfite or sodium sulfite is kept in a closed air-tight container, then this stabilizer is effective in preventing decomposition. However, when the suspension is open to the atmosphere, the sulfite or hyposulfite, rapidly loses its stabilizing efiects. Commercially, of course, it is completely impractical to manufacture or store the bisdithiocarbamates inv an oxygen-free condition.

' The decomposition of salts of alkylene bisdithiocarbamic acids appears to be an oxidative reaction since the decomposition is greatly reduced, if not completely stopped, in the absence'o'f oxygen or air. Thus, decomposition was substantially prevented when samples of manganese ethylene bisdithiocarbamate were stored in a dry nitrogen atmosphere.

The decomposition of metal salts of alkylene bisdithiocarbamic acids also appears to be catalyzed, in some manner not yet known, by moisture. Thus, it is noted that spontaneous ignition during manufacture is more frequently encountered when the relative humidity is high, and it is generally true that samples with high moisture content are more susceptible to decomposition than samples containing lower moisture content.

It has ben unexpectedly found that if hexamethylene tetramine'is added to manganese ethylene bisdithiocarbamate, the stability of the compound is markedly increased. The amount of hexamethylene tetramine (here- Patented Mar. 7,1961? 3 inafter referred to as hexa) which is required will vary somewhat depending on the specific conditions which ob tain, but from about 0.2% to about 5%, based on the weight of the bisdithiocarbamate, is effective. A preferred embodiment employs from 0.5% to 1.5% of hexa, based on the weight of the bisdithiocarbamate. A particularly preferred embodiment employs 1% hexa based on the weight of the bisdithiocarbamate.

The hexa can be incorporated into the aqueous slurry of manganese ethylene bisdithiocarbamate during manufacture and prior to the drying of the slurry to form the final solid product. Similarly, if the slurry is to be employer per se as a fungicide, the hexa can be added to the slurry at the time of manufacture. It has been found that the hexa is more effective as a stabilizer if it is added to the dried product rather than being added to the slurry. Thus, it is preferred to add the hexa to the dried product, mixing by tumbling, etc.

Biological tests of manganese ethylene bisdithiocarbamate containing 5% hexa with unmodified manganese ethylene bisdithiocarbamate as control showed no difference in fungitoxicity or phytotoxicity. Thus, the presence of hexa does not adversely affect the value of manganese ethylene bisdithiocarbamate as a fungicide.

Manganese ethylene bisdithiocarbamate, as such, and containing one percent hexa, was tested for fungitoxicity against Phytophthora infestans, late blight of tomatoes. In this test, individually potted tomato plants 4 to 5 inches tall (4 leaf stage) were sprayed to the point of run-off with an aqueous suspension of the compound. After the plants were dried, they were inoculated with a spore suspension of Phytophthora infestans containing 30,000 sporangia per ml. The plants were incubated while wet at a temperature of 12 C. for 16 hours. They were then removed from the incubator and held for 48 hours at 25 C. and 50% relative humidity. Treatment performance is read in terms of percentage of leaf area infected and is the mean of four replicates. The average rank reading was calculated according to the following systems:

PERCENT LEAF AREA INFECTED None.

1 Trace (one small lesion). 2 1 to (few lesions). 3 6 to 17%.

A ranking below 2 is considered to be excellent. The results of the test were as follows:

Lb./100 Gallons Compound it Mo Has ethylene bisdithiocarbamate.

forth in Table I. It should be noted that Sample 1, the

Processes for the preparation of manganese ethylene bisdithiocarbamate are well-known in the prior art. One method of preparation is set forth in US. 2,504,404. The method set forth therein comprises the preparation of disodium ethylene bisdithiocarbamate by the reaction of sodium hydroxide, ethylene diamine and carbon disulfide in aqueous solution. Manganese chloride in aqueous solution is then added to the aqueous solution of disodium ethylene bisdithiocarbamate and the manganese ethylene bisdithiocarbamate which precipitates is recovered by filtration or centrifugation. It is subsequently dried and, if necessary, ground to fine particle size. Similarly, preformed disodium ethylene bisdithiocarbamate may be employed by dissolving it in water and adding an aqueous solution of a manganese salt to the dissolved disodium ethylene bisdithiocarbamate. The prep aration of the manganese ethylene bisdithiocarbamate forms no part of the present invention. I

As set forth hereinbefore, biological tests have proven that the manganese ethylene bisdithiocarbamate containing even as much as 5% hexa is quite as effective as the unstabilized manganese salt. In a sense, it is actually true that the addition improves its value as a fungicide by virtue of preventing loss of active fungicidal ingredient and it does not alter the type of fungicidal activity exerted by the compound. Furthermore, the hexa-stabilized manganese ethylene bisdithiocarbamate exhibits the same order of low phytotoxicity and the same degree of safety that is characteristic of the unstabilized material. The methods of use of the non-stabilized manganese ethylene bisdithiocarbamate are well-known and typical fungicidal preparations are set forth in US. Patent 2,504,404. The stabilized manganese ethylene bisdithiocarbamate of the present invention can be employed in exactly the same manner as the unstabilized salt is. There need be no change in method of application or in the application rate.

The stabilities of the samples were tested by subjecting them to heat at a given temperature in a closed system while being swept constantly by a stream of humidified air. Any exotherm which develops during the test is re corded on a differential recorder which records the difference between the temperature of the sample and the temperature of the bath. The air which is swept over the sample is bubbled through a trap containing a solution of lead acetate to collect any hydrogen sulfide that may be evolved and through a methanolic potassium hydroxide trap to collect the carbon disulfide which is evolved.

The stability tests were conducted at two temperatures, at C. and at 70 C. The 90 C. tests were considered to be accelerated screening tests, while the 70 C. tests were conducted to simulate the most adverse conditions to which the products might be naturally subjected, i.e., without the application of artificial heat sources. This temperature, 70 C. (158 F.) is commonly used by the Armed Forces as the maximum temperature to which their supplies will be subjected unless an artificial heat source is applied thereto.

Data on a series of tests conducted at 90 C. are set decomposition, but this value, when considered in conjunction with the value for the exotherm peak and the presence or absence of charring, does give an accurate appraisal of the amount of decomposition. It is important also to note that even as little as 0.25% hexa completely prevented charring. It is also evident from 'Table I that as little as 0.25% hexa substantially decreased the exotherm peak. The very marked reduction of carbon disulfide evolution and reduction in the exetherm peak by the presence of 0.5% of hexa is indicative of the very high elfectiveness and the specificity of hexa as a stabilizer for manganese ethylene bisdithiocarbamate.

Table I EFFECT OF HEXAMETHYLENE TETRAMINE AT 90 0.

Sample No 1 2 a 4 5 Method 01 A i i n Dry- Dry- Dry- Dry- Mtxed Mixed Mixed Mixed Concentration HMT pereent.. None 5 1 0. 5 0. 25

' (control) Exotherm:

Maximum temperature differen- V tial 0... 53 2.3 2 5 4.0 20 Time to peak -.hrs.- 2% 1% 1% GB, Evolved:

Total CS "mg" 1, 607 151 172 431 1, 860

Total Time hrs. 6 22 23 24 16 Appearance Charred Not Not Not Not charred charred charred charred l HMT is hexamethylene tetramine. I 6 hours.

As would be expected, the rate of decomposition at 70 C. was appreciably slower than at 90 C., but the stabilizing eifect of hexa was still evident even at the lower temperature as shown by the data in Table II.

Table II EFFECT OF HEXAMETHYLENE TETRAMINE AT 70C.

Sample No 1 2 Method of Addition Dry-Mixed Concentration Hexa percent. None 1 (control) Exotherm (Maximum Temperature Difierential) 0-. 5 3 to 5 GS; Evolved (Mg.):

04 hrs 127 93 53 2O 21 11 25 6 14 2 60 2 144 11 87 24 I claim:

1. A composition resistant to decomposition on ageing comprising manganese ethylene bisdithiocarbamate having intimately admixed therewith a stabilizing amount of hexamethylene tetramine.

References Cited in the file of this patent UNITED STATES PATENTS 2,665,285 Johnson Jan. 5, 1954 2,791,605 Dorman et al. May 7, 1957 2,860,870 Beauchamp Sept. 17, 1957 OTHER REFERENCES Hazen et al.: Insecticidal Aerosols, Soap and Sanitary Chemicals, August 1946, pages 151, 153 and 155. 

1. A COMPOSITION RESISTANT TO DECOMPOSITION ON AGEING COMPRISING MANAGANESE ETHYLENE BISDITHIOCARBAMATE HAVING INTIMATELY ADMIXED THEREWITH A STABILIZING AMOUNT OF HEXAMETHYLENE TETRAMINE. 